In systems with stationary derrick structures with multiple well centers, conventionally equipment for each well center is duplicated and operated independently. Each well center thus has its own equipment configured to provide support for operations on only one drill line for one well center. Shortcomings mentioned here are only representative and are included simply to highlight that a need exists for improved derrick structures. Embodiments described herein address certain shortcomings but not necessarily each and every one described here or known in the art.